Update (March 15): Shortly after this post was originally published, the situation at the Fukushima Daiichi facility worsened dramatically: there was an explosion at a third reactor, which may have damaged the containment unit there, along with a new fire. Reports elsewhere now suggests that more radioactive material escaped, but the extent of the risk of further release of radioactivity is not yet clear. The title of the post has been edited to reflect the changing situation. (Original title: “Relax: Fears Of Japan’s Radioactive Leakage Are Overblown”)

A second explosion hit Japan’s Fukushima Daiichi nuclear power plant today and authorities are preparing to pump seawater into a third imperiled reactor. But considering that Friday’s earthquake was seven times more powerful than the maximum limit they were designed to withstand, we’re lucky the situation isn’t much worse. Japan’s scenario is a far cry from Chernobyl: Any radioactive leakage that has occurred is low, and unlikely to affect anyone outside the local area (if that).

What Happened

Both today’s explosion (in reactor No. 3) and the one on Saturday (reactor No. 1) have the same cause: a breakdown in the cooling system as tsunami waters swamped generators. Specifically, today’s explosion was caused by hydrogen gas, which builds up as the seawater that’s pumped in to cool the reactor also heats up. From video footage, the explosion looks devastating, and while 11 people were injured, the steel and concrete containment shell around the nuclear reactor was not damaged—which is the main reason why authorities say the situation is mostly under control. “There is no massive radioactive leakage,” Cabinet Chief Cabinet Secretary Yukio Edano told the New York Times. Here’s a rundown on the risks in the leakage that has occurred:

What Is Escaping (and How)?

The root problem is heat: Even though the nuclear chain reaction is safely stopped in all of Japan’s nuclear reactors, that doesn’t stop heat from building up.

The uranium “stopped” the chain reaction. But a number of intermediate radioactive elements are created by the uranium during its fission process, most notably Cesium and Iodine isotopes, i.e. radioactive versions of these elements that will eventually split up into smaller atoms and not be radioactive anymore. Those elements keep decaying and producing heat. Because they are not regenerated any longer from the uranium (the uranium stopped decaying after the moderator rods were put in), they get less and less, and so the core cools down over a matter of days, until those intermediate radioactive elements are used up. [The Energy Collective]

The radioactive particles that are entering the environment are mostly planned escapes: Workers vent steam to release pressure as the reactors heat up the water. And while some report low levels of radioactive cesium and iodine, the majority are radioactive nitrogen, which don’t pose much of a health hazard:

By the time you spelled “R-A-D-I-O-N-U-C-L-I-D-E”, they will be harmless, because they will have split up into non radioactive elements. Those radioactive elements are N-16, the radioactive isotope (or version) of nitrogen (air). The others are noble gases such as Xenon. But where do they come from? When the uranium splits, it generates a neutron (see above). Most of these neutrons will hit other uranium atoms and keep the nuclear chain reaction going. But some will leave the fuel rod and hit the water molecules, or the air that is in the water. Then, a non-radioactive element can “capture” the neutron. It becomes radioactive. As described above, it will quickly (seconds) get rid again of the neutron to return to its former beautiful self. [The Energy Collective]

So What’s The Risk?

We don’t know exactly how much radioactive material has been released, but we do know that only very low levels have been detected around the plant.

The IAEA has described it as a level four event on the International Nuclear and Radiological Event Scale (INES), which is used for an accident “with local consequences”. No abnormal levels of radiation have yet been detected in Russia. [BBC]

The radioactive nitrogen decays in seconds, and therefore seems to pose no threat. Other radiactive elements are not so innocuous:

Radioactive iodine could be harmful to young people in the vicinity of the plant. After the 1986 Chernobyl nuclear disaster there were some cases of thyroid cancer as a result. People who were promptly issued with iodine tablets ought to be safe, however. Radioactive caesium, uranium and plutonium are harmful, but do not target any particular organ of the body. [BBC]

These iodine tablets help fight radiation by making sure your body has all the iodine it needs: With sufficient iodine levels, your body won’t need to absorb any more, which in this case, would be radioactive iodine. According to Josef Oehmen, a research scientist at MIT:

There was and will *not* be any significant release of radioactivity. By “significant” I mean a level of radiation of more than what you would receive on – say – a long distance flight, or drinking a glass of beer that comes from certain areas with high levels of natural background radiation. [The Energy Collective]

Yet despite the low risk, tens of thousands of people have been evacuated around the plants for precaution, and the U.S. moved an aircraft carrier after it detected low-level radiation 100 miles offshore.

No Comparison to Chernobyl

The reactors in Japan are built to a much higher standard than the ones that led to the 1980s Chernobyl incident.

At Chernobyl an explosion exposed the core of the reactor to the air, and a fire raged for days sending its contents in a plume up into the atmosphere. At Fukushima the explosions – caused by hydrogen and oxygen vented from the reactor – have damaged only the roof and walls erected around the containment vessels. [BBC]

In Japan, all nuclear chain reactions have been successfully stopped, and all the explosions occurred outside the reactors’ containment vessels—so there is no major risk of significant radioactive leakage.

What’s Next?

According to Oehmen, the normal cooling water will gradually replace the the seawater coolant, and like any nuclear reactor fuel change, workers will dismantle the core and haul it to a processing facility. But it will probably take five years to check the entire plant for damage, and with the inspection of its nuclear power station, Japan’s power generating abilities will probably be reduced by about 15%—not nearly as bad what could have happened if the earthquake had damaged Japan’s nuclear plants more seriously.

Unfortunately, although the Japanese government say that the reactor No. 3 was undamaged, it seems that there is still some doubt about that.
Although i am not a nuclear expert i would be quite surprised that the reactor core was not damaged in some way from the hydrogen explosion. And i would not exclude the possibility that we may still have exposed reactor core.

Paul

What reaction causes the hydrogen gas to form? I wouldn’t think it would be as simple as heating up the seawater that gets pumped into the reactor. Do you know?

Thanks!

St.Averti

It’s curious how everyone is alarmed by the shut down of a few nuclear reactors, that for all intents and purposes were undamaged by such a violent earthquake. No one seems to care about the petrochemical plants that are ablaze though; those didn’t even last through the quake let alone the tsunami. So while everyone is afraid of a few radioactive species coming from more or less unscathed reactors, the petrochemical plants that are burning to the ground sit happily releasing Uranium, Radon and Tritium; plus a myriad of non radioactive pollutants into the air. Do we have our priorities straight or what?

Jason

One huge omission. The spent fuel rods. These are outside containment and exposed to the air. (These are located to the upper right of the containment vessel in the illustration. ) The pool must cover and cool the spent fuel rods. Any cracks or leaks in the pool could uncover the spent fuel which can heat and catch fire. If the spent fuel catches fire… you have your Chernobyl.

The pool may have been damaged in the earthquake, the hydrogen explosion, or the subsequent collapse of the roof structure. Unit3 is especially vulnerable as it experienced a more powerful hydrogen explosion which damaged the outer walls directly adjacent to the spent fuel pools.

This is far from over.

crf

It may have come from reaction of water with the zirconium steel alloy coating the fuel pellets. This is the working assumption. If the core heats up enough (which is will do, if uncovered with water), then this can happen.

The steam + hydrogen is in the reactor core, and is then released from the core into the reactor containment building (so it is outside the core). It would be very mildy radioactive from reaction of elements in seawater while they were in the reactor. From what I read, not enough to harm anyone when vented outside the building, most likely, but certainly very measureable. But they had to use seawater, because the traditional cooling pumps with de-ionized water failed for multiple different reasons (this will all get hashed out later).

Normally, the water they use is deionized water, very clean ordinary water, which contains no salts, like sea or tap water does. So there is nothing to get radioactive, even as it bathes the core. Venting de-ionized water steam releases, mostly, small amount of tritium. This isn’t concerning. In a normally working reactor, such water is kept in a closed loop, and not exposed to the environment. It enters the core, cools the reactor, exits the core, is cooled in a cooling loop, then goes back into the reactor again. This looping-cycle failed, when the backup generators to run this pumping and cooling cycle failed (plus it may have failed for other reasons).

More seriously, because the core was uncovered, the rods’ coating and fuel may have melted, which means that when they circulate the sea water within the cores, and vent the steam from it, more concerning radio-isotopes of uranium and its fission byproducts may be released.

Even more seriously, there are reports that they are still having trouble pumping seawater into the reactors at a high enough rate to keep the cores covered until they cool down. Due to pressure (pumping into a high pressure vessel is hard) and due to possible earthquake/tsunami/hydrogen-explosion damage.

As long as they are able to get water to cool the reactor, a full meltdown will not happen. The pressure vessel is also built to contain a meltdown. So whatever happens, release of truly harmful amounts of radiation into the environment are not likely.

Also, because the situation is happening slowly, it may be possible to mitigate a meltdown, should it occur, by working outside the containment vessel.

At Fukushima Daiichi unit 3, the explosion was an indicator of serious problems inside the reactor core.

Victor Gilinsky, a former commissioner at the Nuclear Regulatory Commission, said that to produce hydrogen, temperatures in the reactor core had to be well over 2,000 degrees and as high as 4,000 degrees Fahrenheit. He said a substantial amount of fuel had to be exposed at least at some point.

The Fukushima Daiichi unit 3 was built by Toshiba. Last year, the unit began using some reprocessed fuel known as “mox,” a mixture of plutonium oxide and uranium oxide, produced from recycled material from nuclear weapons as part of a program known as “from megatons to megawatts.” Anti-nuclear activists have called mox more unsafe than enriched uranium. If it escapes the reactor, plutonium even in small quantities can have much graver consequences on human health and the local environment for countless years, much longer than other radioactive materials

Dennis

“We don’t know exactly how much radioactive material has been released, but we do know that only very low levels have been detected around the plant.”

In fact, we only know figures the Japanese government chooses to make public. Perhaps the author of this article can visit the nuclear plants and take his/her own measurements to back up his theory. After all, radiation leakages at these sites are overblown, and governments never withhold information from the public.

SilenceIsGolden

Well said, Dennis. And, please: Who is “The Energy Collective” that’s so copiously referenced/sourced here? I can’t find much background information, except for a short reference to mega-company Siemens — who by no means could be considered independent. It’s further said: “Our members are our content contributors, and include leading scientists, activists, policy makers, executives and entrepreneurs.” So, wouldn’t it have been more appropriate to cite HERE which one of those contributors contributed?

http://hankroberts.wordpress.com Hank Roberts

Time to correct the main post:

“US ships in Japan reposition as 17 crew members exposed to radiation
9 hours ago
… ships and aircraft away from the quake-damaged Fukushima Dai-Ichi Nuclear … The aircraft carrier was operating about 100 miles northeast of the power …”

“A THIRD explosion in four days has shaken Japan’s earthquake-damaged Fukushima nuclear plant, as authorities struggle to prevent a catastrophic release of radiation.

Japan’s nuclear safety agency said an explosion was heard today at Fukushima’s No 2 reactor, where it was revealed last night that fuel rods had become fully exposed, sparking fears of a new blast.

The explosion, reported at 6:10am local time (8.10am AEDT), was the latest in an alarming build-up of events at the No 2 reactor, now the main focus of Japan’s nuclear safety crisis.

The evolving emergency has cast a shadow over the efforts of the government to provide relief in the country’s northeat, where the death toll from Friday’s massive quake and ensuing tsunami is expected to exceed 10,000.

Today’s explosion was feared to have damaged the reactor’s pressure-suppression system, the Nuclear and Industrial Safety Agency said, citing information from operator Tokyo Electric Power Co. [that’s the “torus” and explains the “hole in the bottom” reported earlier–hr]

Radiation levels at the plant rose quickly again following the reported explosion and the agency said it was concerned radioactive material might be leaking from the reactor.

TEPCO was reported to be evacuating workers from the Fukushima nuclear plants.

Chief Cabinet Secretary Yukio Edano told reporters there had been no sudden jump in radiation indicators.

However Kyodo News reported that higher radiation levels had been recorded today in a region north of Tokyo following this morning’s blast.

Earlier today Mr Edano said the reactor’s containment vessel might have been damaged, raising the risk of uncontrolled radiation release.

A defect had been detected in the vessel, he told reporters, and the reactor “was not necessarily in a stable condition”.

Separately, a NISA official said the suppression pool under the reactor core, which holds spent fuel rods, might have been damaged.

Fuel rods in the No 2 reactor, now the most seriously worrying of the three reactor units damaged by Friday’s magnitude 9,0 earthquake, became exposed for a second time early this morning.

TEPCO began trying to pump seawater back into the damaged reactor core about 3am but the pressure build-up within was making pumping difficult.

At one stage late last night, after the four-metre fuel rods were fully exposed and apparently began melting, radiation levels at the plant reached 3,130 microseiverts hourly, six times the allowable limit.

Earlier yesterday there was an explosion in the No.3 reactor building, apparently caused by hydrogen build-up, but authorities said the containment vessel had not been breached. There was a similar explosion at the No 1 reactor on Saturday…..”

botmosa

Hey Patrick,
Your source has no expertise in nuclear power–he’s a supply chain management specialist. Plus, this info is so out-of-date. Isn’t this supposed to be a science blog? Can’t you find someone who actually knows about nuclear power? The situation is still slipping away from the plant staff, and you tell us to “Relax”! If there’s anyone who wants to understand what’s going on, don’t bother coming to this place.

M.S. Patterson

I am really tired of endless alarmism surrounding these events.
As St. Averti pointed out, there are far more dangerous and environmentally damaging situations playing out around Japan right now.

The reactors will shut down with small releases of some radioactive material, but nothing major, and these will rapidly be diluted and much of them will decay in relatively short order.
Much more nuclear material was released during open air bomb tests.

It’s not the end of the world, people.

Jason

“Ah, this is obviously some strange usage of the word ‘safe’ that I wasn’t previously aware of.”
–Arthur Dent in “The Hitchhikers Guide to the Galaxy”

Bob

“You keep using that word. I do not think it means what you think it means”
–Inigo Montoya in “Princess Bride”

delbert norvin

um, no, not really.

one of the commenters here sniffed how he is “so tired” of reading about the alarmism in the press. well, nobody wants to be alarmist. but i, for one, am equally tired of you pseudo scientific snobs poo-poo-ing any and all discussion of potential worst-case scenarios. and, as the news in the last several hours reveals, you all have been proved wrong. things are getting much, much worse.

so maybe it’s time to redraft that silly headline?

just sayin’

Cathy

Even if this is a “worst case scenario” there’s nothing we can do here on a blog except wring our hands in despair. So the calls to chill out are warranted. If you want to do something proactive and responsible, go buy stocks in renewable energy.

John Lerch

I wonder about the claim that the reactors endured an earthquake 7 times more powerful than they were designed to stand. I.E. the reactors here in the US and in the rest of the world endured Japan’s earthquake also. So surely the level of earthquake that they were designed to endure must be an earthquake at that level right under the reactor rather than a 100 miles away. By which criterion they did not endure the maximum.
It’s annoying that the reporters here at Discover seem to accept stuff without much discrimination. If they do dig deeper, they should explain so instead of printing spin.
And indeed St. Averti’s comment is totally appropriate too. Journalists should be investigating that also.
Bottom line. Any failures here aren’t failures of nuclear science–they’re failures of political science, of managerial science and of prior investigative journalism.
Actually 2nd bottom line. Everyone wants to have their cake and eat it too. If we paid for the ramifications of burning petrochemicals, gasoline would cost infinity. (That’s the only way the amount spent on gasoline/year would stay constant even when the petro is all gone–infinity *zero=amount spent today.)

scott

although i am not a huge fan our major sources of energt (i do like my lifestyle, but…i think we could have done better by now, that’s all) the oil industry will milk the publics fear on this to secure new drills and getting new support for their own expansion into sensitive areas, most likely causing much more damage over the long term than this.

as everyone here in LA is salivating in panic over this, they dont stop to think of the thousands of gallons of oil, tons of trash and tons of soot that are expelled onto the roads (then waterways to the sea), sidewalks, streets and air each day, and what daily impact that has on their health and that of the nation.

http://Sry,you'renotinvited Blob

Hum.
Yeah, i thought i was a bit premature to ‘Relax’. The Japanese are still trying to cool and stabilise the cores and possible molten nuclear pools. Just now, Reactor 4 seems to be a the next problem. But, as someone who has actually been inside a nuclear plant i think the ‘danger’ is mostly over…mostly.

(Place Aliens Quote here)

Amos Zeeberg (Discover Web Editor)

Thanks for your sharp eyes and feedback. I think this post presented a decent snapshot of the publicly available information when we published (and took into account more sources than were quoted), but in retrospect, the story was too much in flux to try to pin it down with the degree of certainty we depicted. We’ll come back to the topic when it’s settled down some, and will consider many of the points raised here.